Currently available evidence indicates that digestive enzyme zymogens such as trypsinogen become prematurely activated within acinar cells of the pancreas during the early stages of acute pancreatitis. Activated digestive enzymes are believed to cause cell injury leading to acinar cell death and pancreatitis. The proposed project will pursue the following specific aims: 1) to define the mechanisms responsible for premature activation of zymogens within the pancreas and the role of those activated digestive enzymes in the evolution of acute pancreatitis; and 2) to determine if the type of acinar cell death (ie, necrosis or apoptosis) during acute pancreatitis regulates the severity of that acute pancreatitis. The specific aim #1 studies will build on the observation that infusion of a supramaximally stimulating dose of the CCK analog caerulein causes intrapancreatic activation of trypsinogen as well as pancreatitis in rats. Furthermore, cathepsin B mediated activation of trypsinogen occurs when isolated acini are incubated in vitro with supramaximally stimulating concentrations of caerulein. In the proposed studies, the intracellular location of trypsinogen activation, the cellular events involved in trypsinogen activation, and the mechanism by which trypsinogen activation leads to cell injury will be determined. In the specific aim #2 studies, several models of experimental pancreatitis in laboratory animals (mice, rats, opossums) will be utilized to evaluate the possibility that apoptosis minimizes the severity of pancreatitis. The mechanisms underlying this phenomenon will be examined and the potential value of treating established pancreatitis by inducing apoptosis will be evaluated. Successful completion of these proposed studies will provide important new insights into the cellular basis for acute pancreatitis and identify methods of either preventing or minimizing the severity of this frequently lethal disease.